Piston pump for delivering hydraulic fluid in a block-protected vehicle braking system

ABSTRACT

A piston pump for the delivery of hydraulic fluid, in particular for ABS braking systems, comprises a pump housing 10 with an inlet 12 and an outlet 14 for the hydraulic fluid. A piston 16 is guided in the pump housing 10 without a sliding sleeve and supplies hydraulic fluid from the inlet 12 to the outlet 14 of the housing 10. A valve assembly 20 together with the piston 16 and a return spring 34 for the piston is joined as an asseembly capable of being handled independently and arranged directly in the pump housing 10.

FIELD OF THE INVENTION

The invention relates to a piston pump for delivering hydraulic fluid,particularly in a block-protected vehicle braking system.

BACKGROUND OF THE INVENTION

When using such a pump in a block-protected braking system (ABS) and/oran anti-slip control (ASC) system of a vehicle, its purpose is to supplyhydraulic brake fluid to the master cylinder and/or the vehicle wheelbrakes, in order to achieve a braking action within the ABS or ASCcontrol cycles in a known manner.

In such piston pumps according to the state of the art, the intake andoutlet valves are generally arranged in the longitudinal axis of thepump. These pumps are referred to as radial piston pumps. A pistonperforms working strokes along the longitudinal axis of such a pump inorder to supply the hydraulic fluid towards the brake of the vehicle. Inaccordance with the state of the art, the piston is accommodated in asliding sleeve which is securely connected with the pump housing, andthe intake and outlet valves are usually arranged on the longitudinalaxis of the pump. This state of the art is known from DE-A-32 36 536,DE-A-37 42 824 and DE-A-40 27 794.

SUMMARY OF THE INVENTION

In the case of this state of the art, the piston, the intake valve and areturn spring for the piston must each first be installed in a slidingsleeve which keeps the components together. The sliding sleeve with saidinstalled parts can then be inserted as a sub-assembly into the housingof the valve. Such a design of the piston pump is intricate with respectto the number of components and their assembly.

The invention is based on the object of further developing a piston pumpof the initially mentioned type in such a manner that the effortrequired for manufacturing and assembly is reduced.

According to the invention, this object is solved in that certain partsof the piston pump are designed in such a way that they can be connectedwith each other prior to assembly in the pump in such a manner that theyform an assembly which is capable of being handled independently. Inorder to form this assembly, the piston as well as individual parts ofthe valve are preferably taken into consideration. The return springwhich biases the piston towards a drive unit can also be added to theassembly which is connected with the piston prior to installation in thepump by means of a positive connection.

The invention also makes it possible to reduce the manufacturing andassembly effort for a piston pump in that the sliding sleeve which isused in the state of the art is omitted and instead of which the pistonand the valve assembly are capable of being installed directly in thepump housing. The "direct" installation of said parts in the pumphousing means that no special sliding sleeve is arranged between thepiston and the valve assembly and the housing which encloses theseparts. This inventive solution of said object does not necessarily implythat the piston, the return spring and the valve assembly have beenconnected to form an independently handable assembly prior toinstallation in the piston pump.

It is preferably intended to have the assembly (consisting of at leastthe piston, the valve assembly and the return spring, if required)connected by means of a part of the valve assembly.

The component which permits the connection of the assembly is preferablya shaped sheet metal part of the valve assembly.

The inventive handling of the components piston, intake valve and returnspring as an independent subassembly of the piston pump is advantageousin that an easy and primarily position-independent assembly is possible,because this subassembly can be inserted directly into the pump body(housing) without prior installation in a sliding sleeve and without acertain positioning of the housing.

The connection of said components to one another is preferably effectedby means of positive connections and elastic engagement of the partsinto each other.

The design of the component which connects said parts as a shaped sheetmetal part is advantageous in that such a shaped sheet metal part can bemade by means of a punching or bending process. Through holes for thehydraulic fluid can be provided directly in the shaped sheet metal partthrough a corresponding shape of the sheet metal part. The shaped sheetmetal part preferably serves as a spring cage of the valve assembly. Inthe case of the state of the art, such spring cages are usuallymanufactured by means of a deep drawing process or a die castingprocess, and the through holes for the hydraulic fluid must be made inan additional operation, which increases the manufacturing effort andthus the costs.

The above-mentioned inventive measures not only enable simplification ofmanufacturing and assembly of the piston pump, but, in addition, alsosimplification of the disassembly of the piston pump because fewer partshave to be removed and removal is further simplified in that several ofthe components can be removed from the piston pump in a connectedcondition as an independently handable assembly.

In another preferred embodiment the piston and the shaped sheet metalpart are designed in such a manner that the shaped sheet metal part ispositively retained by the piston. This can be achieved, for example, bya radially projecting collar or retaining rim which is positivelyembraced by the shaped sheet metal part.

In an advantageous embodiment, the piston comprises at least one seal atits circumference which seals the piston against a hole in the housing,in which the piston is guided in a slidably movable manner. For thispurpose, the piston is preferably provided with a shoulder whichaccommodates the seal, with the seal in the assembled condition beingbiased by the return spring towards the shoulder. If the shaped sheetmetal part has several arms, of which at least one is angled in a radialdirection (outwardly or inwardly) at its free end, these free ends canpress the seal onto the shoulder of the piston under the biasing forceof the return spring. This results in a stable and secure seat of theseal on said shoulder.

In the following an embodiment of the invention will be explained inmore detail with reference to the drawing, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a piston pump in two differentoperating conditions;

FIG. 2 shows a plan view of a shaped sheet metal part for use in apiston pump according to FIG. 1 before its final forming operation;

FIG. 3 shows a section along line A--A in FIG. 2;

FIG. 4 shows a side view of a finished formed sheet metal part;

FIG. 5 shows an axial plan view of a shaped sheet metal part accordingto FIG. 4;

FIG. 6 shows a detail according to FIG. 1 in an enlarged scale;

FIG. 7 shows a detail from FIG. 6 in an enlarged scale; and

FIG. 8 shows an assembly of a piston pump according to FIG. 1 in twodifferent operating conditions of the intake valve in a secondembodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

According to FIG. 1, a piston pump comprises a housing 10 which formsthe pump body. The purpose of the pump is to deliver hydraulic fluid ina vehicle braking system, particularly in an ABS and/or ASC brakingsystem.

The hydraulic fluid reaches the housing 10 via an inlet 12 and isdischarged from the housing 10 under pressure by means of the pump to avehicle brake (not shown).

A piston 16 is supported in the housing 10 in such a manner that it ismovable along the longitudinal axis A of the pump such that a sealingaction is maintained. A drive 18 moves the piston 16 in the housing 10.In a known manner an eccentric serves as the drive 18, which pressesagainst a face 16a of the piston 16 via a stop face 18a and therebymoves the piston to the left (in FIG. 1). FIG. 1 shows two differentpositions of the components. Below the longitudinal axis A of the pistonpump, the piston 16 and the components which move together with it areillustrated in a first extreme position E1 in which the components arein their furthest right hand position in the drawing, while thecomponents above the longitudinal axis A are in their furthest left handsecond extreme position E2.

A valve assembly 20 is connected with the piston 16.

A seal is arranged between the piston 16 and a central hole 21 in thehousing 10, in which the piston 16 is movably arranged.

Via the inlet 12 and a passage 24 the hydraulic fluid to be deliveredreaches an inner chamber 26 which is formed in the piston 16. At theface end of the piston 16, when viewed in the direction of delivery, avalve seat is formed against which a ball 28 can be placed in anaccurately fitting (sealing) manner.

A shaped sheet metal part 32 is attached at the piston 16. The shapedsheet metal part 32 and its fastening at the piston 16 will be explainedlater in a more detailed manner with reference to FIGS. 2 to 7.

A return spring 34 biases the piston 16 to the right (FIG. 1), i.e.towards the drive 18. The return spring 34 is positively engaged withthe shaped sheet metal part 32 as will also be explained later in a moredetailed manner with reference to FIGS. 6 and 7.

Downstream of the ball 28 which serves as a valve closing member achamber 36 is formed in the housing 10 for accommodating hydraulicfluid. The shaped sheet metal part 32 is provided with passages (seealso FIGS. 4 and 5) so that a permanent sliding connection between theinterior of the shaped sheet metal part 32 and the chamber 36 isprovided.

A valve body 38 is securely (unmovably) connected with the housing 10and has a central channel 40 through which the hydraulic fluid can flowto the left in FIG. 1 (in the direction of delivery) if a ball 42 opensa seat at the outlet of the channel 40 against the force of a spring 46.The hydraulic fluid then flows via a channel 44 to an outlet 14.

An end piece 48 is also rigidly connected with the housing 10 and formsa cage for the spring 46. The flow path to the outlet 14 is sealed bymeans of a seal 50.

The piston pump according to FIG. 1 operates as a suction pump. In theextreme position E1 of the piston 16 as shown in FIG. 1 below thelongitudinal axis A, hydraulic fluid is present in the inner chamber 26of the piston. If the piston 16 is then moved by means of the drive 18in a delivery stroke into the extreme position E2 (positions 18' of thedrive or 16', respectively, of the piston) as shown in FIG. 1 above thelongitudinal axis A, the ball 28 remains sealingly on the associatedvalve seat 30 and the hydraulic fluid in the chamber 36 is subjected toa high pressure due to the piston movement. This pressure moves the ball42 against the force of the relatively weak spring 46 so that thehydraulic fluid flows to the outlet 14 via the passages 40, 44 and isthus supplied under high pressure to the vehicle brake. After the pistonhas reached the extreme position E2 as shown in FIG. 1 above thelongitudinal axis A the eccentric drive returns into the extremeposition E2 (this is the initial position) so that the piston 16 isforced to the right due to the relatively high biasing force of thereturn spring 34. In this case, the ball 42 is in sealing contact withits associated seat on the valve body 38. Upon movement of the piston 16to the right in FIG. 1, the force of the spring 34 causes a vacuum inthe chamber 36 (which is filled with hydraulic fluid) so that the ball28 is lifted off the valve seat 30 and thus makes a flow connection forthe hydraulic fluid between the inner chamber 26 and the chamber 36 (theshaped sheet metal part 32 is provided with openings as alreadyexplained above). Consequently, upon a movement of the piston 16 fromthe left to the right in FIG. 1, hydraulic fluid flows from between theball 28 and the valve seat 30 into the chamber 36 which, with thismovement, increases its volume. After the piston 16 has reached itsextreme position E1 as shown in FIG. 1 below the longitudinal axis A, anew delivery working stroke of the piston begins due to a movement ofthe eccentric 18 to the left, as described above.

It becomes obvious from the above description that no sliding sleeve asan additional component is arranged between the piston 16 and the valveassembly 20 (which comprises at least the ball 28 with its seat 30 andthe shaped sheet metal part 32) and the hole 21 in the housing 10.

For the assembly of the piston pump (and correspondingly for itsdisassembly) the piston 16 and the valve assembly 20 are connected toform an independently handable sub-assembly. This is described in moredetail in FIGS. 2 to 7.

FIG. 2 shows the shaped sheet metal part 32 prior to its final shaping.It comprises three arms 52a, b, c. In lieu of these, four or more armscan be provided.

The arms of the shaped sheet metal part 32 end integrally in a bottom 54in the centre of which an indentation 56 is provided (see also FIG. 3).

The free ends of each of the arms 52a, b, c are each provided with ahook 60a, b, c for securing the shaped sheet metal part 32 at the piston16 (see also FIG. 6).

The shaped sheet metal part 32 according to FIG. 2 can be punched in asimple manner. The hooks 60a, b, c are made by bending the free ends ofthe arms 52a, b, c.

At a bending point 58 (see also FIGS. 3, 4) the arms 52a, b, c are bentin such a manner that the shaped sheet metal part 32 forms a cageaccording to FIGS. 4 and 6.

Due to the shaping of the shaped sheet metal part 32 as shown in FIGS. 4and 6, a spring seat for a spring 66 which biases the ball 28 towardsthe valve seat 30 is formed at the bending point 58 by means of theindentation 56. The force of the spring 66 is designed in such a waythat with the above described movement of the piston 16 the ball 28 islifted off the valve seat 30 to the right in FIG. 1.

The fastening of the shaped sheet metal part 32 at the piston 16 iseffected by means of the hooks 60a, b, c and a circumferential nose 64of the piston 16. The piston 16 is sealingly guided in the hole 21 ofthe housing 10 by means of a seal 62.

As can be seen from FIGS. 6 and 7, the return spring 34 is slid onto theshaped sheet metal part 32 in such a manner that it can be positivelysecured there and be pulled off the shaped sheet metal part 32 only bythe application of force. For this purpose the shaped sheet metal part32 in its finished bent condition according to FIGS. 4 and 6 is formedin such a way that it is slightly conical and forms a retaining edge 68which is located at such a distance from the hooks 60a, b, c at the freeends of the arms 52a, b, c that one end of the return spring 43 can beslid over the retaining edge 68 and engages elastically in a recessbetween the retaining edge 68 and the hooks 60 (see also FIG. 7) andthus enable the positive attachment of the return spring 34 at theshaped sheet metal part 32.

When assembling the piston pump according to FIG. 1, it is thus possibleto fasten the valve assembly 20, which consists of the shaped sheetmetal part 32, the spring 66 and the ball 28 by means of the hooks 60a,b, c, at the piston 16, and it is also possible to fasten the returnspring 34 at the shaped sheet metal part 32 in the described manner.This does not require a sliding sleeve, and the assembly formed in thisway with the components 16, 18, 66, 32 and 34 can be inserted as a wholeinto the housing 10 of the pump, with no special positioning of thehousing (vertically or horizontally or the like) being required.

FIG. 8 illustrates an assembly of a piston pump according to FIG. 1 intwo different operating conditions of the intake valve in a secondembodiment. Identical parts are given the same reference numerals as inFIG. 1, and in the following their detailed description is omitted.

The seal 62 serves to seal the piston 16 in the hole 21 of the housing10 in a fluid-tight manner in order to ensure the pumping action of thepiston pump. As a result of tolerances, the seal 62 can have both aradial and an axial clearance with respect to the piston 16. The seal 62is accommodated in a shoulder 100 at the end of the piston facing theball 28. In order to ensure maximum life and safe operation the seal 62is preferably made from polytetrafluoroethylene material which enables alow-friction sealing seat in the hole 21, which may be anodized, ifrequired. A seal made from this polytetrafluoroethylene material (PTFE),however, cannot provide for an elastic compensation of the radialclearance. The consequence of this can be that when the pump is runningidle, i.e. with no fluid being supplied, a small fluid quantity willalways remain in the chamber 36, which is compressed by the deliverystroke of the piston 16. This can result in an undesired noise.

As a result of assembly, the radial clearance preferably occurs betweenthe piston 16 and the seal 62. In order to avoid this, the seal 62 isfixed on the shoulder 100 at the piston 16.

At the end of the piston 16 associated with the valve seat 30 thestep-shaped shoulder 100 is provided for radially and axially locatingthe seal 62. At the outer circumference of the valve seat 30 acircumferential surface 110 which is recessed radially inward is formedwhich tapers relative to the foremost end 112 of the piston 16 at anangle of 5° to 35°. Thus, the front end 112 forms a circumferentialretaining edge for the shaped sheet metal part 32. For connecting theshaped sheet metal part 32 positively with the piston 16 or forfastening the shaped sheet metal part 32 in a positive manner at thepiston 16, the shaped sheet metal part 32 is provided with an inwardlyangled portion 114 at its free end, the shape of which corresponds tothe circumferential surface 110. The shaped sheet metal part 32 hasouter ends 116 which project in a radially outward direction and whichare designed in such a way that they urge the seal 62 in an axialdirection into the shoulder 100 if the assembly shown in FIG. 8 isinstalled in the piston pump. This is ensured even in the pressurelesscondition by the action of the return spring 34.

Due to the fact that the seal 62 is biased on the shoulder 100, anadditional sealing is generated which compensates any leakage caused bythe radial clearance between the piston 16 and the seal 62.

For assembly, the seal 62 is slid onto the shoulder 100 at the piston.Subsequently the shaped sheet metal part 32 with the ball 28 locatedtherein is slid over the retaining edge 120 so that the radiallyprojecting ends 116 of the shaped sheet metal part 32 are in contactwith the seal 62. Then the return spring 34 is slid onto the shapedsheet metal part 32 and engages the recess formed by the end of theshaped sheet metal part 32. In this case, the retaining edge 120 of thepiston 16 is embraced in such a way that a positive connection betweenthe shaped sheet metal part 32 and the piston 16 is ensured by thereturn spring. The shoulder 100 and the circumferential surface 110 atthe piston 16 are dimensioned in such a way that the force of pressureof the return spring acts on the seal 62 via the elasticity of the freeends 116 of the shaped sheet metal part 32. Thus, the seal 62 is locatedon the piston 16 also in a radial direction. This ensures that no fluidremains in the chamber 36 with the pump running idle.

We claim:
 1. A piston pump for delivering hydraulic fluid in ablock-protected braking system of a vehicle, comprisinga pump housing(10) with an inlet (12) for the admission of hydraulic fluid into thehousing (10) and an outlet (14) through which the supplied hydraulicfluid leaves the housing (10); a piston (16) guided in a pump housing(10), which carries out working strokes in order to supply hydraulicfluid from the inlet (12) to the outlet (14); a valve assembly (20) inthe delivery path of the hydraulic fluid through the housing (10); adrive (18) which moves the piston (16) through the housing (10) for thepurpose of delivery; and a return spring (34) which biases the piston(16) towards the drive (18), characterized in that the piston (16), thereturn spring (34) and the valve assembly (2) being releasably joined asan independent assembly unit and located in the pump housing (10), thejoined independent assembly unit capable of being retrieved from thehousing (16) as a unit and handled independently.
 2. A piston pumpaccording to claim 1, characterized in that the joining of the assemblyis effected by means of a part (32) of the valve assembly (20).
 3. Apiston pump according to one of claim 1, characterized in that thejoining of the assembly is effected by means of a part (32) of the valveassembly (20).
 4. A piston pump according to claim 3, characterized inthat the shaped sheet metal part (32) can be fastened at the piston (16)by means of at least one hook (60).
 5. A piston pump according to claim3 or 4, characterized in that the shaped sheet meat part (32) ispositively secured by the piston (16).
 6. A piston pump according toclaim 4, characterized in that the shaped sheet metal part (32) ispositively secured by the piston (16).
 7. A piston pump according toclaim 3, characterized in that the part also serves as a spring cage forholding of at least one spring (34, 66).
 8. A piston pump according toclaim 3, characterized in that the part carries the return spring (34).9. A piston pump according to claim 4, characterized in that the shapedsheet metal part (32) comprises several arms (52a, b, c), at least oneof which is provided with a hook (60a, b, c) at its free end forfastening at the piston (16).
 10. A piston pump according to claim 4,characterized in that the return spring (34) is positively secured bythe shaped sheet metal part (32).
 11. A piston pump according to claim4, characterized in that the shaped sheet metal part (32) comprises aretaining edge (68) for positively securing the return spring (34). 12.A piston pump according to claim 1 characterized in that the piston (16)has at least one seal (62) at its circumference, which seals the piston(16) against a hole (21) of the housing (10).
 13. A piston pumpaccording to claim 11 or 12, characterized in that the shaped sheetmetal part (32) comprises several arms (52a, b, c), at least one ofwhich is angled in a radial direction at its free end.
 14. A piston pumpaccording to claim 12, characterized in that the shaped sheet metal part(32) comprises several arms (52a, b, c), at least one of which is angledin a radial direction at its free end.